This application claims the priority of Priority Document P 44 22 202.5, filed in Germany on Jun. 24, 1994 and PCT/DE95/00806, international filing date Jun. 26, 1995, the disclosures of which are expressly incorporated by reference herein.
1. Field of the Invention
The invention relates to a reactor for coating flat substrates as well as to a process for manufacturing flat substrates using reactors of the present invention.
2. Description of the Related Art
Reactors for coating substrates using CVD-processes and particularly MOCVD-processes as well as plasma coating processes require a reaction gas flow through the so-called reactor vessel or reaction vessel in which the substrate(s) to be coated is/are arranged. In order to achieve an excellent coating of the surface of the substrates, it is required to guide the reaction gas flow as uniformly as possible, that is, in a laminar flow so closely past the substrate surface that a layer formation takes place on the substrate which is as homogeneous as possible.
During the manufacturing of xe2x80x9cnormalxe2x80x9d layers, high temperatures are, however, required during the coating process which, among others, have heat convection effects within the gas flow and thus lead to a disturbance of the laminar flow. Although it is possible to increase the laminarity and thus the parallelism of the reaction gas flow relative to the coating surface by means of an increased reaction gas flow rate, transversal flow components may also occur within the reaction vessel caused by convection but also by constructive obstacles which stand in the way of the reaction gas flow. Within the reactor vessel, such transversal flow components lead to the formation of local vortexes which have a negative influence on the coating process.
On the basis of the occurring turbulent flow regions, it can also be explained that the layer formation on the preferably flatly designed substrate does not take place uniformly but that points occur which have a higher layer depositing as well as points which have a lower layer depositing.
In addition, in the case of the known reactor systems, in which the substrates to be coated are arranged on the bottom of the reaction vessel, surface effects occur which are the result of condensate deposits which form on the reactor walls during the coating process and, dependent on the amount of condensate, fall downward from the upper reactor walls and damage the surface of the substrate.
It is an object of the invention to provide a reactor for coating flat substrates and particularly wafers in the case of which a high flow rate is possible while the layer formation is homogeneous, as well as to provide a process for manufacturing such substrates which permits the manufacturing of the most varied substrates.
According to the invention, this object is achieved by means of further developments indicated in the present invention.
The invention is based on a reactor as suggested by Fraunhofer-Gesellschaft zur Forderung der angewandten Forschung e.V.
The three fingers of the vertical receiving arm preferably made of quartz lead out in the downward direction in a common central axis, which is at the same time the axis of rotation for the substrate. This axis is led gas-tightly but rotatably through a lower quartz plate 15, which has larger dimensions than the lower opening of the reactor vessel 9 through which the substrate 2 was introduced into the reactor vessel 9 and closes this opening gas-tightly in the downward direction.
This reactor suggested by Fraunhofer-Gesellschaft, for whose basic construction no protection is claimed within the scope of the present application, has a reactor vessel or reaction vessel into which the reaction gas as well as optionally a carrier gas can be introduced. At least one substrate is arranged in the reaction vessel such that a main surface of the substrate is aligned essentially in parallel to the flow direction of the reaction gases.
For increasing the flow rate, at least two spaces for substrates are provided on the substrate holder unit. The holder or holders is/are constructed in the form of a template which has openings for the surfaces of the substrates to be coated.
According to the invention, the fact is utilized that convective transversal flows within a reactor vessel during the coating operation can be avoided in that the substrate to be coated is mounted in the area of or on the upper vessel chamber such that the main surface to be coated is oriented downward.
In this manner, vortex formations within the flow canal can be excluded. Likewise, because of the substrate orientation according to the invention, the danger of damage as the result of condensate particles impacting on the substrate surface is virtually excluded.
According to the invention, the rotatably disposed carrying ring holding device which holds the substrate contributes to the fact that the reaction gas flow which may have inhomogeneities within the laminar flow rests as uniformly as possible on the substrate surface. This permits a layer formation on the substrate which, on average, is homogeneous.
In principle, the reactor is constructed such that a reactor housing is provided in which the reactor vessel or reaction vessel is contained in which the coating operation takes place. The reaction gases flow through the reactor vessel within a closed loop and in the process coat the substrate surfaces entered and mounted inside the reactor vessel. The reactor housing, in turn, is connected with a transfer canal housing which has a cassette housing in which the substrates are arranged which are to be coated and which, as required and for reasons of a fully automated coating sequence, store the substrates. A cassette charger is provided, in which the substrate surfaces can be deposited together with their associated carrying rings.
Furthermore, the cassette housing can be connected to a transfer canal housing mounted directly on it. The connection between the transfer canal housing and the cassette housing as well as the cassette housing and the reactor housing takes place by gas-tightly closing valves so that it is ensured that the operator of the system will not come in contact with the gas-atmospheric conditions inside the reactor vessel.
The above described reactor is suitable for the production of the most varied materials. Specifically, not only III-IV-layers can be produced but also II-VI-semiconductor layers, SiC, SiGe, oxides, superconducting materials, etc.
In this case, the process pressures may be below or above 100 mbar.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.